Image forming apparatus with accommodation spaces

Abstract

A laser printer is detachably provided with a carrier belt, support rollers for supporting the carrier belt, and a belt unit provided with a belt frame. A unit support portion for supporting a bearing portion of the support roller and a unit support portion for supporting a bearing portion of the support roller are provided at a side of the main body of the apparatus. Urging by a coil spring allows the bearing portion to press the unit support portion against the support roller. An image forming unit that contains four process cartridges is detachably provided above the belt unit opposite to the belt. The belt unit may be removed from the main body by detaching the image forming unit.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 a main body having an opening formed in a side portion, which contains a first accommodation space able to communicate with said opening and a second accommodation space able to communicate with at least said first accommodation space; and 
 a first unit detachably installed in said first accommodation space within said main body through said opening; 
 a second unit detachably installed in said second accommodation space within said main body through said opening and comprising a belt unit including:
 a belt; 
 a plurality of support rollers provided with at least first and second support rollers for supporting said belt; and 
 a frame portion that retains said support rollers, wherein 
 
 said second unit is detached and attached through at least a portion of said first accommodation space between said second accommodation space and said opening. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein: said first unit is an image forming unit having a plurality of photosensitive drums arranged in a direction perpendicular to an axial direction of said photosensitive drums; and a guide member that slides along a linear direction formed by connecting at least two axes of said plurality of photosensitive drums to guide said image forming unit. 
     
     
       3. The image forming apparatus according to  claim 1 , wherein:
 said belt unit is provided with a reference protrusion having a constant positional relationship with said first support roller; 
 said main body is provided with a first locate member including a first wall portion that supports said reference protrusion from one side and a first abutment portion provided at a side different from that of said first wall portion, and an urging member that applies an urging force such that said reference protrusion and said second support roller move away from each other; and 
 said first locate member is structured such that an angle formed by a wall surface of said first wall portion and a wall surface of said first abutment portion is smaller than 90°, and said belt unit is located at an installed position by supporting said reference protrusion between said first wall portion and said first abutment portion under said urging force applied by said urging member. 
 
     
     
       4. The image forming apparatus according to  claim 3 , wherein said reference protrusion comprises a bearing portion that bears said first support roller. 
     
     
       5. The image forming apparatus according to  claim 4 , further comprising a second locate member, wherein: said second locate member includes a second wall portion that supports said second support roller from one side, and a second abutment portion that supports said second support roller from a side different from that of said second wall portion; and said second support roller is supported in a state where an angle formed by a wall surface of said second wall portion and a wall surface of said second abutment portion is smaller than 90°. 
     
     
       6. The image forming apparatus according to  claim 5 , wherein a virtual plane formed by connecting said reference protrusion and a rotary shaft of said second support roller is substantially in parallel with a wall surface of said first wall portion, and said first abutment portion has a wall surface inclined to said virtual plane. 
     
     
       7. The image forming apparatus according to  claim 6 , wherein a force is applied to said second support roller in a direction away from said reference protrusion under said urging force applied by said urging member. 
     
     
       8. The image forming apparatus according to  claim 7 , wherein:
 a first gear is provided at a shaft portion of said first support roller; 
 a second gear is provided for transferring a drive force to said first gear; and 
 a force directed toward said second support roller and said first wall portion is applied to said shaft portion of said first support roller in accordance with a drive force transferred from said second gear to said first gear. 
 
     
     
       9. The image forming apparatus according to  claim 3 , wherein:
 a rotary shaft is provided such that it protrudes at an end portion of said frame portion of said belt unit, which is opposite to said opening, and a support portion is provided at a side of said main body for supporting said rotary shaft; and 
 an end portion at said opening of said belt unit is pivotally driven into an accommodation space for said belt unit such that said reference protrusion moves away from said first locate member. 
 
     
     
       10. The image forming apparatus according to  claim 8 , wherein:
 said belt unit includes an electrically connectable terminal portion, and an electric part to which an electric power is supplied from outside said belt unit via said terminal portion; 
 said second gear applies a thrust force along at least said shaft portion of said first support roller to said first gear; and 
 an external terminal portion that is electrically connected to said terminal portion while urging said terminal portion in a same direction as that for applying said thrust force is provided in said main body to which said belt unit is installed. 
 
     
     
       11. The image forming apparatus according to  claim 10 , wherein:
 a shaft portion of said second support roller is supported at a planar surface; 
 said urging member urges a shaft portion of said second support roller along said planar surface in a direction away from said reference protrusion; and 
 a wall surface of said first wall portion is in parallel with said planar surface. 
 
     
     
       12. The image forming apparatus according to  claim 1 , wherein:
 said belt unit is provided with a first bearing member that bears said first support roller and includes a first reference protrusion, and a second bearing member that is moveably attached to said frame relative to said first bearing member to bear said second support roller and includes a second reference protrusion; 
 said main body is further provided with: 
 a first locate member including a first wall portion on which said first reference protrusion is positioned, and a first abutment portion that abuts against said first reference protrusion at a plane opposite to said second reference protrusion; 
 a second locate member including a second wall portion on which said second reference protrusion of said second bearing member is positioned, and a second abutment portion that abuts against said second reference protrusion at a plane opposite to said first reference protrusion; 
 an urging member that moves said second abutment portion of said second locate member to apply a tensile force to said belt; and 
 a release mechanism that is brought into a released state in which said second abutment portion is moved against an urging force of said urging member upon reception of an operation force. 
 
     
     
       13. The image forming apparatus according to  claim 12 , wherein said second reference protrusion comprises a bearing portion that is positioned adjacent said second support roller of said second bearing member. 
     
     
       14. The image forming apparatus according to  claim 13 , wherein said first reference protrusion comprises a bearing portion that bears said first support roller of said first bearing member. 
     
     
       15. The image forming apparatus according to  claim 13 , wherein said first reference protrusion is provided at a position closer to said second reference protrusion of said second bearing member than a bearing portion of said first bearing member. 
     
     
       16. The image forming apparatus according to  claim 15 , wherein said belt unit is accommodated in said main body, and a distance between upper end sides of said abutment portions of said first and second locate members is longer than a distance between said first and second reference protrusions when said release mechanism is in a located state where said release mechanism is not in said released state. 
     
     
       17. The image forming apparatus according to  claim 16 , wherein said belt unit is accommodated in a body casing, and an angle formed by said first wall portion and said first abutment portion is smaller than 90°, and an angle formed by said second wall portion and said second abutment portion is smaller than 90° in a located state where said release mechanism is not in said released state. 
     
     
       18. The image forming apparatus according to  claim 17 , further comprising a retention mechanism that retains said release mechanism in said released state. 
     
     
       19. The image forming apparatus according to  claim 18 , wherein:
 said second abutment portion is rotatably supported at a side of said body casing against an urging force of said urging member; 
 said retention mechanism includes a press member that eccentrically rotates in response to said operation force so as to be allowed to press said second abutment member; and 
 said press member presses said second abutment portion when said release mechanism is in said released state, and a pressing force contains a component against a rotating component of said second abutment portion of a restoring force of said urging member. 
 
     
     
       20. The image forming apparatus according to  claim 19 , further comprising a release lever that applies said operation force to said release mechanism in response to a predetermined operation, wherein an operation load of said release lever required for releasing said release mechanism is equal to or less than half of a load applied to said second reference protrusion of said second bearing member by said urging member in a located state where said release mechanism is not in a released state. 
     
     
       21. The image forming apparatus according to  claim 19 , wherein:
 pairs of said second locate member and said release mechanism are provided at both ends of said belt unit so as to interpose said belt unit; and 
 said release mechanism is integrally provided with said release lever, said release lever applies said operation force to said release mechanism at both sides. 
 
     
     
       22. The image forming apparatus according to  claim 21 , wherein said release mechanism is operated in association with an opening operation of an opening and closing cover provided to said body casing and is opened and closed for detachment and attachment of said belt unit. 
     
     
       23. The image forming apparatus according to  claim 22 , wherein
 a drum unit that includes an image carrier disposed opposite to said belt is detachably accommodated in said body casing; and 
 said release mechanism is operated in association with an attachment and detachment of said drum unit. 
 
     
     
       24. The image forming apparatus according to  claim 23 , wherein:
 said second abutment portion is rotatably supported at a side of said body casing against an urging force applied by said urging member; 
 said release mechanism rotates eccentrically in response to said operation force, and includes an operation lever allowed to press said second abutment portion; and 
 said operation lever presses said second abutment portion when said release mechanism is in a released state, and a pressing force contains a component of a restoring force of said urging member against a rotating component of said second abutment portion. 
 
     
     
       25. An image forming apparatus comprising:
 a main body provided with a cover member that is opened and closed to cover an opening formed in a side portion; 
 a belt unit including an endless belt, a plurality of support rollers including at least first and second support rollers for supporting said belt, and a frame portion that retains said support rollers, which is detachably installed in said main body through said opening; 
 a reference protrusion including a constant positional relationship with said first support roller, provided to said belt unit; 
 a locate member provided in said main body and including a first wall portion that supports said reference protrusion from one side, and an abutment portion provided at a side different from that of said first wall portion, which is structured such that an angle formed by a wall surface of said first wall portion and a wall surface of said abutment portion is smaller than 90°; and 
 an urging member provided in said main body and applying a force such that said reference protrusion and said second support roller move away from each other and said reference protrusion is interposed between said first wall portion and said abutment portion. 
 
     
     
       26. An image forming apparatus comprising:
 a main body provided with a cover member that is opened and closed to cover an opening formed in a side portion; 
 a belt unit including a belt, a plurality of support rollers including at least first and second support rollers for supporting said belt, and a frame portion that retains said support rollers, which is detachably installed in said main body through said opening, wherein: 
 said belt unit is further provided with a first bearing member that bears said first support roller and includes a first reference protrusion, and a second bearing member moveably attached to said frame relative to said first bearing member and includes a second reference protrusion; 
 said main body is further provided with 
 a first locate member including a first wall portion on which said first reference protrusion is positioned, and a first abutment portion that abuts against said first reference protrusion on a plane opposite to said second reference protrusion; 
 a second locate member including a second wall portion on which said second reference protrusion is positioned, and a second abutment portion that abuts against said second reference protrusion on a plane opposite to said first reference protrusion; 
 an urging member that moves said second abutment portion of said second locate member so as to apply a tensile force to said belt; and 
 a release mechanism that is brought into a released state in which said second abutment portion is moved against an urging force applied by said urging member in response to an operation force. 
 
     
     
       27. The image forming apparatus according to  claim 26 , wherein said first locate member is structured such that an angle formed by a wall surface of said first wall portion and a wall surface of said first abutment portion is smaller than 90°.